Composition and process for making leather



atented'Apr. 2, 194 l COMPOSITION AND PRQCESS FOR MAKING LEATHER I No Drawing. Application August 11, 1987, Serial No. 158,510

6 Claims. ('Ci. 149-5) This invention relates to processes for tanning hides to make leather, and is particularly directed to tanning processes wherein a soluble titanium compound, preferably titanium sulfate, is introduced into hides as a Werner complex in acidic solution and there precipitated in situ by reducing the acidity.

It has long been known that titanium compounds have a tanning action on hide substances,

19 but the use ofv titanium compounds as tanning agents has met with little commercial success because of difllculties encountered in applying such compounds to commercial tanning processes. One great diiiiculty arises from the fact that the titanium compounds which are known to have a tanning action unfortunately are unstable in the presence, of hide substances and are so readily precipitated that it has heretofore been impossible to secure adequate penetration of the ti- 20 'tanium into hides. Such premature precipitation of the titanium results in incomplete and nonuniform tanning, only the surface of the hide being adequately tanned.

I have found that titanium compounds can v satisfactorily be used to make leather by introducingthem into hides in the form of a Werner complex in acidic solution and by then effecting precipitation and combination of the titanium compound with the hide in situ by reducing the so acidity.

In acidic solution a Werner complex'of a soluble titanium compound such as I employ in the initial step of a tanning process according to my invention is stable even in the presence of hide substances. Accordingly when hides are immersed in such a tan liquor the titanium tanning agent is enabled to penetrate thoroughly into the hide, and uniform tanning. even of theinterior of the hide, is assured.

When hides thus treated with a titanium tanning agent are subsequently treated with an acidneutralizing substance inv accordance with my invention, the titanium compound precipitates clearly understood from the following illustrative example.

Example 2.8 parts of a 50% lactic acid solution and 26.3 15

parts by weight of a titanyl sulfate solution containing 9.5% total T10: and 24.2% total S04.

Immediately following the addition of the tan liquor parts of water containing 0.66 part of sodium carbonate was added. This mixture was drummed for 15 minutes, after which 1.26 parts of powdered sodium aluminate was added. The

skins were then drummed in this mixture for 2 hours to allow the titanium tanning agent to penetrate thoroughly into the leather. 25

After penetration of the leather by the titanium tanning agent had taken place, the acidity of the tan liquor was reduced to allow fixation of the titanium compound. This acidity reduction was effected by, adding sodium carbonate and water so at intervals, the drumming. being continued between additions. Over a period of 5 hours a total of 3.6 parts of sodium carbonate and 22.6 parts of water were added. The pH of the final solution was 3.9. 85

The tanned leather was finished off by draining, shaving, and fatliquoring in accordance with the usual practice.

The leather of this example was white in color, had a smooth grain. a plump and firm quality, 0

and a pleasing feel. The leather retained these characteristics after aging for several months. The appearance of the leather and its freedom from change upon aging indicated that satisfactory tanning had taken place.

Examination-of the spent tan liquors from the above example indicated that substantially all of the titanium tanning agent originally present had been incorporated into the' leather. The amount of titanium compounds which had therefore been takenup by the leather was a further indication that satisfactory tanning had taken place.

These indications of complete and thorough tanning were further substantiated by a shrink test in which samples of the tanned leather from the above example were immersed in water and the water was heated. The tanned leather of this example was found to withstand temperatures of from 75 to 85 C. before shrinkage took place, whereas the untanned hides shrank badly at from 40 to 45 C., and samples of titanium tanned leather made by processes other than those of the present invention shrank at temperatures of from 45 to 65 C.

As will be seen from the above example, a Werner complex of a soluble titanium compound in acidic solution is introduced into suitably prepared hides according to the processes of my invention. When the titanium is associated with the other constituents of the tan liquor as a Werner complex in acidic solution, as in the above example, it has but little tendency to react with or to be precipitated by the hide substances, whereas if unassociated and free to ionize it would be readily precipitated by the hide substances.

Complexes of titanium for use in my novel tanning processes may be made by causing a soluble titanium compound to react in acid solution with any suitable substance capable of coordinating with titanium according to the Werner theory to form soluble compounds from which the titanium does not readily dissociate. Substances which are known to form Werner complexes with chromium are illustrative of the type of compounds which I may employ in conjunction with titanium.

More particularly, organic acids such as formic, acetic, butyric, lactic, oxalic, tartaric, or citric acids or their salts may be used to form Werner complexes. Lactic acid, as used in the above example, is preferred because the lactic acid salts formed by neutralization with such alkalies as bases of the alkali metals or ammonia do not crystallize upon drying out and therefore give the leather a somewhat softer, smoother feel than is obtained with acids whose salts crystallize upon drying.

The amount of an organic acid or its salts which must be used to make a Werner complex of titanium for leather treatment according to a process of my invention depends somewhat upon the soluble titanium compound used and also upon the degree to which it is desired to inhibit combination of the titanium with hide substances. With titanyl sulfate and lactic acid,-

as used in the above example, from about to 1 mol of lactic acid per mol of combined titanium gives satisfactory results. The proportions used in the above example comprised about /2 mol of lactic acid per mol of combined titanium.

As the source of the titanium for making a Werner complex of the type employed in my novel tanning processes I may use any titanium compound which is soluble in acid solution and does not have a deleterious effect on the leather produced. Such commercially available solutions as titanium sulfates or chlorides are suitable, the titanyl sulfate solution of the above example being typical of such products.

The pH of the initial tan liquor used in a process of my invention is determined by such factors as the degree of hydrolysis of the titanium compound employed and upon the buffering action of the substance added to form the Werner complex of titanium. If the pH is too low, the free acid will have a deleterious effect upon the leather, and if the pH is too high, there is danger that premature precipitation of the titanium will take place. I prefer to employ a solution having a pH in the range of from about 1.5 to about 2.5, and more preferably, of about 1.9.

The acid neutralizing substance which I may employ in my novel titanium tanning processes may be any substance which satisfactorily ties up the free acidity and raises the pH of the system. As a practical matter, alkalies, because of' their low cost .and ready availability, are to be preferred. Such materials as lime, caustic soda, or ammonia may be used.

I have found, however, that a combination of sodium carbonate and sodium alurninate such as used in the above example produces leather of unusually good quality, partly because this combination seems to give the optimum conditions for neutralization of free acid and partly because the sodium aluminate itself functions to a certain degree as a tanning agent.

The amount of acid-neutralizing substance The rate at which acid-neutralizing substances are added in the processes of my invention is determined by the time required for such sub stances to penetrate into the hides. The time required is in turn determined by suchfactors as the thickness of the hide, the acid-neutralizing substance used, and the degree of agitation. It is preferred to add a small amount of the acid-neutralizing substance and to work this amount into the hides before adding further amounts. The above example illustrates Such procedure, although a process wherein the acidneutralizing substance was continuously added would also give. the desired condition. The tanning drum used in the above example provided a practical means for accomplishing the necessary agitation of the hides during the tanning process.

The processes of my invention are applicable to the tanning of hides and skins of various kinds. Such skins as calf skin, pig skin, and kid skin are examples of materials which I may employ in making leather by my novel titanium tanning processes.

The manner of preparing the hides or skins will depend, of course, upon the use for which the finished leather is intended. The calf skins of the above example were intended for use in shoe uppers, and accordingly had been limed and unhaired and pickled in a 1.5% sulfuric acid solution containing about 10% of salt as is the customary practice in the art. When my novel proc-' esses are used for tanning fur, the liming and unhairing step are, of course omitted,

The step of drumming the hides in salt solution prior to tanning employed in the above example was used for the purpose of loosening up the hides and rehydrating them to make them take up the tannin more readily, as has already ways without departing from the spirit of my invention.

I claim:

1. In a process for tanning hides to make leather, the steps comprising introducing, in acidic solution, a Werner complex of a soluble titanium sulfate with a compound of the group consisting of organic acids and their salts, and then precipitating an insoluble titanium compound from the Werner complex in situ in the hides by reducing the acidity.

2. In a process for tanning hides to makeleather, the steps comprising introducing, in acidic solution, a Werner complex of a soluble titanium sulfate with a compound of the group consisting of organic acids and their salts, and then precipitating an insoluble titanium compound from the Werner complex in situ in the hides by adding an alkali to reduce the acidity.

3. In a process for tanning hides to make leather, the steps comprising introducing, in

acidic solution, a Werner complex of a soluble titanium sulfate with a compound of the group comprising organic acids and their salts, and then precipitating an insoluble titanium compound from the Werner complex in situ in the hides by I adding an alkali containing sodium aluminate.

4. In a process for tanning hides to make 'leather, the steps comprising introducing, in

acidic solution, a Werner complex of titanyl sulfate with lactic acid and then precipitating an insoluble compound from the Werner complex in situ in the hides by adding an alkali to reduce the acidity.

5. In a process for tanning hides to make leather, the steps comprising treating the hides at an acidity from about pH 1.5 to 2.5 with a solution of 8. Werner complex of titanyl sulfate with about one-fourth to one mol of lactic acid per mol of combined titanium, then precipitating an insoluble titanium compound from the Werner complex in situ in the hides by adding an alkali to reduce the acidity.

6. In a process for tanning hides to make leather, the steps comprising treating the hides at an acidity from about pH 1.5 to 2.5 with a solution of a Werner complex of titanyl sulfate with about one-fourth'to one'mol of lactic acid per mol of combined titanium, then precipitating an insoluble titanium compound from the Werner complex in situ in the hides by adding sodium carbonate and sodium aluminate to reduce the acidity to about pH 3 to 4.

JOHN V. VAUGHEN. 

